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Biochem-708 MOLECULAR BIOCHEMISTRY
3(3-0)
Structural organization of genes and chromosomes in prokaryotes
and eukaryotes, nucleosomes, properties of DNA and RNA in
solution. Replication of DNA: Replication theory and semiconservative replication, molecular mechanism of replication in
prokaryotes and eukaryotes. Enzymes involved in replication.
Molecular nature of mutations, DNA damage and repair. Modification
and restriction. Transcription: synthesis and processing of RNA.
Reverse transcription and RNA replication in viruses. Genetic code
and Wobble hypothesis. Translation, essential factors, enzymes,
initiation, elongation and termination of protein synthesis. Posttranslational modifications and targeting of proteins. Control of
transcription and translation. Regulation of gene expression in
prokaryotes.
Recent advances in biotechnology and genetic
engineering.
SUGGESTED READINGS
•Berg, J.M., J.L. Tymoczko and L. Stryer. 2007. Biochemistry, 6th
ed. W.H. Freeman and Company. New York.
•Nelson, D.L and M.M. Cox. 2008. Lehninger Principles of
Biochemistry. 5th ed. Worth Publishers, New York.
•Old, R.W. and S.B. Primrose. 1995. 4th ed. Principles of Gene
Manipulation: An Introduction to genetic Engineering. Blackwell
Scientific Publications, London.
•Sambrook, J. F., Russell, D. W. and Irwin, N. 2000. Molecular
cloning: A laboratory manual, 3rd ed. Cold Spring Harbor
Laboratory press, Cold Spring Harbor, N.Y.
•Singer, M. and P. Berg. 1991. Genes and Genomes. University
Science Books, Nill Valley, California.
•Voet, D. , J.G. Voet and C. W. Pratt. 2006 . Fundamentals of
Biochemistry. 2nd ed. John Wiley and Sons. Inc. New York.
•Weaver, R. F. 2008. Molecular Biology. 4th ed. McGraw Hill
Higher Education.
DNA as genetic material
Chromosomes are comprised of two types of
macromolecules, proteins and DNA, but which one is
the stuff of genes?
12.1 The Griffith Experiment
– the answer was discovered from a variety
of different experiments, all of which
shared the same basic design
• if you separate the DNA in an individual’s
chromosomes from the protein, which of the
two materials is able to change another
individual’s genes?
Frederick Griffith in 1928 experimented with
pathogenic (i.e., disease-causing) bacteria
– he experimented with two strains of
Strepococcus pneumonia
12.1 The Griffith Experiment
• the virulent strain, called the S form, was
coated with a polysaccharide capsule and
caused infected mice to die of blood poisoning
• a mutant form, called the R form, which lacked
the capsule and was non-virulent
Griffith determined that when dead bacteria of the S
form were injected into mice, the mice remained
healthy
But, when Griffith injected12.1mice
with mixture of dead
The Griffith Experiment
S bacteria and live bacteria of the R form, the mice
unexpectedly died
– the R form bacteria now had transformed
into the virulent S variety
Figure 12.1 How
Griffith discovered
transformation
Oswald Avery,
Colin MacLeod and Maclyn McCarty
The agent responsible for transforming
Streptococcus went undiscovered until a classic
series of experiments by Oswald Avery and his
coworkers Colin MacLeod and Maclyn McCarty
– they also worked with Streptococcus
strains, both dead S and live R, but were
able to remove first nearly 99.98% of the
dead S
– they found that the transforming principle
was not reduced by the removal of the
protein
The Avery team discovered that the
transforming principle resembled DNA in
several ways
– same chemistry and behavior as DNA
– not affected by lipid and protein extraction
– not destroyed by protein- or RNA-digesting
enzymes
– destroyed by DNA-digesting enzymes
Based on this overwhelming evidence, the
Avery team concluded that the heredity
material was DNA
Alfred Hershey and Martha Chase
experiment
Alfred Hershey and Martha Chase provided
the final experimental evidence that pointed
to DNA as the hereditary material
– the team studied viruses that infect bacteria
– the structure of these viruses is very simple: a
core of DNA surrounded by a coat of protein
– the viruses attach themselves to the surface of
bacteria cells and inject their genes into the
interior
• the infected bacterial cell is then forced to make
hundreds of copies of new viruses, which then burst out
of the cell to infect new cells
Hershey and Chase used radioactive isotopes to
“label” or tag the DNA and the protein of the viruses
– some viruses were grown so that their
DNA contained radioactive phosporous
(32P)
– other viruses were grown so that their
protein coats contained radioactive sulfur
(35S)
The Experiment
After the labeled viruses
were allowed to infect
bacteria, only the viruses
with 32 P had labeled tracer
in their interior
The conclusion was that the
genes that viruses use to
specify new viruses are
made of DNA and not
protein
Components of
Nucleic acids
In order to understand how DNA functioned as the
molecules that stored heredity, researchers needed
to understand the structure of DNA
– DNA is comprised of subunits called
nucleotides
– each DNA nucleotide has three parts
• a central dexoyribose sugar
• a phosphate group
• an organic base
Erwin Chargaff and his colleagues
in the late 1940s
1. The base composition of DNA generally varies from
one species to another.
2. DNA specimens isolated from different tissues of
the same species have the same base composition.
3. The base composition of DNA in a given species
does not change with an organism’s age, nutritional
state, or changing environment.
4. In all cellular DNAs, regardless of the species the number
of adenosine residues is equal to the number of the
thymidine residues (that is, A : T), and the number of
guanosine residues is equal to the number of cytidine
residues (G : C)
Thus: the sum of the purine residues equals the sum of the
pyrimidine residues; that is, A+G:T+C.